There's a good summary of NPR Labs' recent HD test in the latest Radio World:
http://www.rwonline.com/article/89178I attended Mike and John's preliminary presentation in Philadelphia last month -- and from what I saw, I think the tests were conducted very well, yet (not surprisingly) iBiquity has already questioned NPR's credibility.
I would be much more inclined to question the "tests" conducted by Clear Channel at WKCI in Connecticut which, of course, showed no problem with the full 10 dB power increase (refer to the recent thread started by radioskeptic.)
Some questions I would ask are:
1) Were the elevated digital carriers transmitted from the same (main) antenna as the analog signal?
2) If not, is the digital (aux) antenna mounted on the side of the tower, rather than on a pole at the top?
3) If side-mounted, is it attached to the east leg? The first-adjacent stations WPDH and WCBS-FM are to the west, so the tower would likely reduce radiation in that direction several dB, lessening interference to those stations. And although the FCC considers both antennas to be "non directional", anyone who has been in this business for a few years understands the effects of side-mounting (and Clear Channel probably uses this to their advantage better than anyone else!)
4) Can we see some measurements showing how the two patterns compare on the west side?
Meanwhile, here are some photos of WKCI's tower to review:
http://www.necrat.us/wkci_pro.html
